1. Field of the Invention
This invention relates to an image reading apparatus.
2. Description of the Related Art
Among image reading apparatuses such as copy machines and the like, some apparatuses are known to have a capability to select between two types of document reading manners. A first document reading manner is a fixed document reading mode by a flat bed scanner (FBS), in which a document placed on a platen is read while moving a reading unit placed thereunder. A second document reading manner is a conveyance document reading mode, in which a document auto-fed by an automatic document feeder (ADF) is read by a reading unit fixed at a predetermined position. In the conveyance document reading mode, a large amount of papers with a predefined size can be automatically read efficiently. Similarly, in the fixed document reading mode, a document which is difficult to be conveyed such as a book or a 3D object can be read.
Normally in an image reading apparatus having the two modes described above, a motor, for example, as a driving source for the ADF is required, and aside from this, another motor, for example, as a driving source for moving the reading sensor is required. Similarly, two drivers in total to drive these driving sources are required, so that it has become one factor contributing to an increase in cost of an apparatus.
Therefore, an apparatus has been proposed, in which a driving source for the ADF and a driving source for moving the reading unit are combined into one, and these are driven by a single driving source. For example, in Japanese Patent Laid-Open No. 1-266529, an apparatus is proposed, in which a motor is shared and units to which a driving force is transmitted are switched by an electromagnetic clutch. However, since an electromagnetic clutch is a relatively expensive mechatronic part, a large cost reduction is not easily realized. Therefore, apparatuses in which the number of mechatronic parts is reduced are proposed in US-2008-0266614 and in Japanese Patent No. 3810643, compared with the apparatus proposed in the Japanese Patent Laid-Open No. 1-266529.
However, in the configuration described in US-2008-0266614 and in the Japanese Patent No. 3810643, the conveyance direction of a document by an ADF is restricted to one direction. When the conveyance direction of a document is restricted to one direction, a recovering operation after document jam processing, or reverse conveyance for a skew correction (registration) of a document cannot be performed. Similarly, in order to add a two-sided reading function, reverse conveyance becomes necessary to reverse the document. Therefore, the performance of a product needs to be necessarily degraded, such as cutting some functions that the apparatus can perform.
The reason why the conveyance direction of a document is restricted to one direction resides in that a driving target of the driving force of a motor serving as a common driving source is switched between an ADF and a mechanism to move a reading unit by the drive force of the motor itself. In this configuration, when the motor is rotated in the direction to reversely convey the document, the transmission destination of the driving force is returned to the mechanism to move the reading sensor, so that the conveyance direction cannot to be switched.